[Darryl Ramm]

Thanks for sharing your results.

The difference in speed you are seeing is the actual magic of this adapter card. The PCIe switch on the card is doing PCIe 2 to PCIe 3 link aggregation, turning pairs of slower PCIe 2 lanes in the Mac Pro into a PCIe 3 lane, and doing that across 8 down to 4 lanes. This sort of lane aggregation happens down at the PCIe hardware level so is possible to just work with different devices, with maybe some exceptions, but in this case does not care about AHCI vs NVMe... they are higher level disk protocols running over PCIe. Most M.2 PCIe slot adapter cards have no switch at all, they are dumb a rock and just directly wire the slot lanes to the M.2 connectors. Which is why they can cost ~$20 each.

And to make it clear to folks the older model number AHCI drive being discussed is the Samsung SM951.

With PCIe 4 SSDs starting to appear, we will likely end up doing similar in future with the PCIe 3 slots in the new Mac Pro cheese graters..